Titanium and alloys of titanium are widely useful materials, in that they have a high hardness, a high strength to weight ratio at elevated temperatures, a relatively low thermal conductivity, exceptional resistance to corrosion, and they are stronger in compression than in tension. Such materials are used extensively in the aerospace industry and are now quite commonly used where the harsh environments of heat or corrosion would have a deleterious affect on structure used in such environments.
The same properties that make the titanium materials useful in industry also make it difficult to form and shape to a desired configuration. The hardness, strength in compression, and low thermal conductivity all make the metalworking of titanium and it's alloys unusually difficult. Such metalworking of titanium includes the removal of material by cutting action and more specifically includes the drilling of holes or apertures in the body of titanium material.
In normal machining of steels or other materials, a large part of the heat generated by the cutting or shearing of the material is contained in the chip and carried away from the work area as the chip flows past the drill point. Because titanium has a low heat conductivity much of the heat generated by the cutting or shearing action is not carried away by the departing titanium chips resulting in temperatures at the cutting surface ranging from 1000 degrees F. to 2000 degrees F. In addition the drill point cutting surfaces may be experiencing pressures of 200,000 to 300,00 PSI.
In the past the drills that have been available for drilling of titanium have used cutting edges that either present a negative cutting action to the material to be removed or a drill point configuration that extrudes the material before a positive cutting action can be presented to the work piece. The center material is to be removed from the work piece by drilling is referred to as the web and it is desirable that it be removed by a cutting action rather than an extruding action.